Closed loop reactant/product management system for electrochemical galvanic energy devices

ABSTRACT

The present invention teaches a closed loop energy system including means capable of managing both cooling cycle and the fuel/oxidant gas flow in conjunction with a fuel cell. The system includes a plurality of galvanic cells, gas flow conduit means, internal fluid flow conduit means, heat exchanger means, liquid-gas separator means, and gas repressurization means.

This is a continuation of application Ser. No. 07/739,627 filed Aug. 2,1991, now U.S. Pat. No. 5,192,627.

This invention is directed generally to a closed loop system for themanagement of hydrogen-oxygen fuel cells. More specifically, thisinvention is directed to a low temperature hydrogen-oxygen fuel cellrequiring cooling water and gas flow management.

BACKGROUND OF THE INVENTION

Fuel cells are galvanic systems which operate following similarelectro-chemical principles as in conventional storage batteries. Thereis a Positive and negative electrode separated by an ion-conductingelectrolyte adapted to carry current generated by a catalyzed chemicalreaction. The fuel cell, however, has a theoretically infinite poweroutput capability, as long as fuel and oxidant are continuously fed tothe system for reaction. For example, the current flow in thetraditional hydrogen-oxygen fuel cell is generally provided by the flowof electrons associated with the passage of an ion through anintervening electrolyte medium.

There are generally three distinct types of low temperaturehydrogen-oxygen fuel cells: the solid polymer proton exchange membranefuel cell,, the alkaline fuel cell, and the phosphoric acid fuel cell.All of these types generally operate at below about 250° C., in aqueoussystems. Electrical energy is produced by the catalyzed reaction betweenhydrogen and an oxidizing gas, usually pure oxygen, with the movement ofan ion, i.e., a proton or hydroxyl ion (OH⁻), through an electrolyteconnecting the positive to the negative electrode. In the alkaline fuelcell, the electrolyte is highly concentrated (at least about 30 wt. %)aqueous potassium hydroxide solution, the concentration determining themaximum operating temperature. This hydroxide electrolyte is generallymaintained within a solid matrix, including, for example, asbestos,together with a catalyst. The catalyst can be, in addition to the noblemetals, nickel, silver, certain metal oxides and spinels.

The second type of low temperature fuel cell is the phosphoric acid fuelcell, which utilizes concentrated phosphoric acid as the electrolyte.This fuel cell operates at temperatures in the range of between 150° C.and just over 220° C. The concentrated acid electrolyte is preferably atapproximately 100% concentration, and is retained in a solid matrix,such as silicon carbide(SiC). The electro-catalyst, which impregnatesboth the anode and the cathode, can be platinum or other such noblemetals.

An efficient low temperature system, which also operates at temperaturesbelow the boiling point of water, includes a solid polymeric protonexchange membrane between the fuel cell electrodes. The membrane isformed from, for example, perfluorocarbon materials sold, for example,under the trademark "NAFION"® by E. I. DuPont De Nemours. A noble metalcatalyst is also required for most polymeric membrane type of fuelcells.

Commonly available solid polymer electrolyte fuel cells require input ofreactant gases, usually a hydrogen fuel and an oxidant, generally oxygenor air, and of water, for cooling and for maintaining the electrolytemembrane.

The cooling systems for the solid polymer electrolyte fuel cells are oftwo types: the water flow, or pass-through, type, where cooling waterfrom outside the cell is provided for indirect heat exchange fromimpervious conduits within the cell; and the passive, or wicking, typeof cell, by evaporative cooling, wherein water is caused to evaporatefrom the anode support plates, which are formed to have a large surfacearea.

For both types of cooling systems, the solid polymer electrolytemembrane must be kept moistened with water; otherwise the membrane willdry out, and become inefficient in operation as well as structurallyweakened. Water is generally carried from the fuel, or hydrogen, side ofthe membrane, together with the proton, through the membrane, therebytending to dry the anode side of the membrane, and causing cracking ofthe membrane. In operation, additional water must thus be supplied withthe hydrogen, to compensate for the water removed.

One system to improve cooling of the fuel cell, while at the same timemaintaining humidification of the fuel side of the membrane, is shown,for example, in U.S. Pat. No. 4,649,091.

As commercially available, the so-called "fuel cell" is actually astacked configuration of a plurality of cells each having an anode and acathode, with a solid electrolyte membrane between them, and passagesfor fuel and oxidant gas. To maintain a continuing operation of such astack of cells requires a system that provides sufficient cooling toprevent overheating of the system and means to provide the fuel and theoxidant, in a managed system to maintain a sufficiently long operatingtime between shutdowns.

In some conventional fuel cell stacks, the hydrogen and oxygen gases aredelivered to the stack in excess of that needed to support theelectro-chemical reaction. There is thus a continuous flow through thestack, and an exhaust from the stack by which product water is removedand any inert gases are vented together with the excess hydrogen andoxygen. Generally, the great majority of the product water is removedwith the oxygen purge, whereas only a relatively small amount ofcondensation is removed along with the hydrogen purge. Generally, thefuel and oxidant gases first pass through humidification cells withinthe cell stack. The gases are there saturated with pure water vapor inorder to prevent dehydration of the ion-conducting membrane. Thehumidified gases are then passed through the anode and cathode chambers,respectively, of the cells within the stack, the cells being fed inparallel; and the excess gases are then vented from the final cell.Although the gas and liquid flow through the stack system is inparallel, i.e., through the individual cells, the electrical connectionbetween the individual cells is conventionally in series.

The cooling water within the stack must be extremely pure, e.g.,deionized water having a high resistivity. The cooling water passesthrough an external indirect heat exchanger where the heat istransferred to, for example, a parallel or countercurrently flowingstream of raw water. This same internal cell cooling water has beenconventionally used to humidify the gas streams within thehumidification stage of the cell stack.

SUMMARY OF THE PRESENT INVENTION

The present invention provides a means to manage both the cooling cycleand the fuel and oxidant gas flow of a fuel cell stack, in a simple andself-adjusting manner. The result of this careful management of such asystem is to provide a greater campaign duration for the operation ofthe fuel cell before shutdown is required, and simultaneously toconserve fuel and oxygen supply for a system of limited fuel capacity,such as on board a submarine. By maintaining all of the products withina closed system, the present invention also precludes the need foradditional ballast control, e.g., for a submarine or aircraft. Finally,the management system further preferably provides for externalhumidification of the system without risking contamination of the fueland oxygen gases, using pure product liquid.

It is therefore an object of the present invention to provide animproved water management system for a low temperature fuel cell stack.

It is the further object of this invention to provide an improved gasflow management system in combination with a water flow managementsystem to provide necessary humidification of the fuel cell electrolyteand while maintaining a sufficiently low concentration of inert diluentwithin the fuel cell system to maintain a long operating period betweenshut-downs.

It is yet a further object of this invention to provide a closed systemfor a fuel cell wherein all reactants and products are maintained withinthe system without loss.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an overall schematic diagram of a preferred system inaccordance with the present invention.

FIG. 2 is a schematic diagram of an alternative system which does notprovide external humidification for the cell gases;

FIG. 3 is a block diagram of the programmable control system for theclosed loop fuel cell stack of the present invention.

FIG. 4 is a top plan view of a fuel cell stack power module inaccordance with the present invention;

DETAILED DESCRIPTION OF THE INVENTION

The present invention, generally, and the systems shown in the figuresof the drawings herewith, are intended to provide a reliable andefficient air-independent power system for such enclosed uses assubmersible vehicles, submerged underwater installations, or spacevehicles, using hydrogen and oxygen as the fuel and oxidant for a fuelcell power source. Most preferably, the present closed loop managementsystem is most effectively used within an enclosed package requiringonly hydrogen and oxygen makeup gas input, external indirect heatexchange, electric power output, and electronic inputs and outputs.

Referring to the system design shown schematically in FIG. 1, a fluidand pressure-tight chamber, the walls of which are indicated by thenumeral 10, contains a fuel cell power source, generally indicated bythe numeral 12, of a relatively low operating temperature type. Mostpreferably the proton exchange membrane type fuel cell is utilized,which operates below the boiling point of water, generally not above 70°to 75° C. There is no requirement to maintain a liquid electrolytebetween the anode and cathode of each cell.

As most generally now configured, the fuel cell power sources areprovided in the form of stacks of fuel cells, literally stacked one nextto the other and having anodes and cathodes arranged in electricalseries. The flow of reactants, i.e., hydrogen and oxygen, to theindividual fuel cells is generally arranged in parallel. As will bediscussed below, it is most effective to utilize a plurality of separatestacks which can continue to operate jointly, albeit at a lower powerlevel, even if a cell in one or more of the individual stacks isincapacitated. By virtue of the configuration of the stacks, theobstruction or inactivity of any individual cell will inactivate theentire stack within which such cell is located.

The power source container 10 is a compact modular assembly which can beinserted, as a unit, into a system requiring a power source, either asthe primary source or as a back-up source of power.

The closed loop management system of the present invention is discussedbelow in terms of a solid polymer membrane electrolyte system whichrequires both cooling and humidification water. In this system, thesupply tanks for the hydrogen reactant and the oxidizing gas, e.g.,oxygen, are located externally of the module container. These fuel andoxidizer tanks can be of standard, or conventional, design such asso-called "gas bottles", containing the gases at pressures of up toabout 2200 to 2500 psig. These bottles are generally equipped withmanual valves and can be connected by known means through the powermodule end plate 85 into the module.

Each of the oxygen and hydrogen gas make-up supply lines 14, 16,respectively, include a solenoid operated valve 17, 18 and a gaspressure sensor (or indicating gauge) 20,21 measuring the gas pressurein each line. Each line further comprises a remotely resettable pressureregulator 24,25, followed downstream by a further gas pressure sensor27,28. The incoming make-up gas lines 14,16 pass into water reservoirs30,31; the gas enters the reservoirs at a lower level, below the waterlevel, so as to bubble through any liquid therewithin for humidificationof the gas. The water reservoirs 30,31 are both pressure-tight so as tomaintain the gas line pressures.

The gas feed lines 33,34 between the reservoirs 30,31 and the fuel cellstack 12, include each a filter 37,38, to remove any solid particles,before passing through a pressure sensor 39,40, respectively, beforeentering the fuel cell stack 12. The design of the flow passages withinthe fuel cell stack is determined by the particular manufacturer of thefuel cells and is not an element of this invention.

Useful such fuel cell stacks include the Ballard Fuel Cell Stack, havingan overall volume of approximately 1.5 cubic feet and weighing about 100pounds. Such a fuel cell stack is stated by the manufacturer to contain42 cells and is capable of generating 5 kilowatts utilizing hydrogen andoxygen. The fuel cell membrane electrolyte can be a sulfonatedfluorocarbon, such as NAFION, manufactured by DuPont.

Such a fuel cell can operate continuously at an internal temperature ofabout 70° C., with respect to the cooling water, but can start-up atroom temperature, producing about 85% of rated power at that temperatureat full constant voltage. The stack can warm up within a few minutesfrom the heat generated by the fuel cell. Accordingly, the cooling wateris not required to be directed to the heat exchanger, until the desiredoperating temperature is reached. The fuel cell can be operatedcontinuously or intermittently at the full range of power from 0% to100%.

By replacing NAFION with a new sulfonated fluorocarbon membrane made byDow Chemical, current densities have been increased to 4000 amps per sq.ft. at cell voltages in excess of 0.5 volts per cell, thus giving powerdensity in excess of 2 kilowatts per sq. ft.

Other useful fuel cells of the solid membrane electrolyte type areshown, for example, in U.S. Pat. Nos. 4,175,165; 4,795,536; 4,678,724;and 4,826,741. Although the latter patent obtains hydrogen from a metalhydride source, the fuel cell operating on the generated hydrogen gaswould be effective in the present system.

After flowing through the fuel cell stack, the excess remaining hydrogenand oxygen gases exit the stack through outlet piping 50,51,respectively. The pressure of these excess gases must be increasedbefore the gas can be recycled. In this embodiment, the gases are eachrepressurized by the gas recycle pressure pumps 54,55.

These recycle pressure pumps 54,55 can be powered by the electricaloutput from the fuel cell, as part of the "hotel load" on the fuel cell.As an alternative to such an electrically powered recycle pump, aneductor type system can be employed, utilizing the gas flow from the gassupply bottles. This reduces the usage of electricity without in any waydiluting or contaminating, or otherwise interfering with the reactantgas flow.

A check valve 57,58 is provided in each return gas line 50,51,respectively, to prevent any backflow; and a gas flow sensor 60,61 isprovided in each line 50,51 to measure the recycle gas flow in eachline. The recycle gas lines 50,51 then connect to the upper portion ofthe water reservoirs 30,31, where the recycle gases are mixed with themake-up gases from lines 14 and 16.

In this embodiment, the upper portion of each of the water reservoirs30,31 comprises the free space above the water level in the reservoir,and each such free space acts as a liquid-gas separator, any liquidwater drops out while the gas is resident in the free space, separatingfrom the gas streams, and falling into the lower reservoir section ofthe vessel. There is free gas space above the liquid level, from whichthe now liquid-free, but humidified, gas enters the inlet lines 33,34 tothe fuel cell stack 12. It is understood that other designs, includingseparate liquid-gas separators, e.g., centrifugal separators, can beused, in vessels separate from the reservoirs.

Cooling water must be pure deionized water. Only a relatively smallquantity of water is required at start-up in the water reservoirs 30,31.

The cooling water is pumped from the oxygen water reservoir 30, by awater pump 65, and through lines 64 and 66 into the cooling systemwithin the fuel cell stack 12. The flow of cooling water is measured,preferably at the exit from the fuel stack, by an in-line flow sensor68. Water exits from the cooling system of the fuel cell stack through awater recycle line 70, at which exit point the water temperature ismeasured by temperature sensor 72. The water flows through line 70 to alocation outside of the power package envelope 10, passing through anindirect heat exchange coil 75, which is in contact with any suitablesource of cooling medium, before being returned to the oxygen-side waterreservoir 30. For example, on a submersible or other sea-going vessel,the heat exchanger would be in contact with raw seawater. In othersituations, cooling gases or other liquids, passing through (or over) asuitable heat exchange surface, can be utilized. The design of theindirect heat exchanger 75 is not a part of this invention, and anysuitable design capable of cooling the recycling cooling water to belowabout 40° C. can be used.

The water added to the hydrogen reservoir 31 during operation is aresult of condensation from the recycled hydrogen gas. If desired,additional water can be provided through initial feed/drain line 81, orexcess water can be drained, especially from the oxygen reservoir 30, inthe event a lengthy operating campaign causes the product water level inthat reservoir 30 to increase so that there is inadequate free spacebelow the gas lines 50,33.

Referring now to FIG. 2, a substantially similar system is disclosed,except that the makeup hydrogen and oxygen gases are fed directly fromthe gas supply 4,5 into the stack, without being humidified in the waterreservoirs 130,131. This alternative system requires a humidificationsection in each fuel cell stack to insure against drying out themembrane electrolyte. This is especially onerous in those situationswhere separate fuel cell stacks are operated within the module package;a separate humidification section would be required for each of theseparate stacks in the embodiment of FIG. 2. By utilizing the system ofFIG. 1, wherein all makeup gases are prehumidified, each of the stackscan be further reduced in size and weight by omitting the humidificationsection. As the water reservoir 130 remains a feature of this systemwith or without the prehumidification effect, the reduction in weightand volume of the fuel cell stack and the overall power package isclear.

By eliminating the internal humidification sections within each cell,for example, in a system utilizing three separate fuel stacks,approximately 20% additional power cells can be obtained within the samevolume and weight.

In addition to improving the efficient use of a fuel cell stack powersource, the closed loop system of the present invention permits a closermanagement of each of cooling water, product storage and gas flowthrough the fuel cell stack. A preferred aspect of any such system isthe use of a system-wide sensing network, having a central logic controlmodule for reading and reacting to data remotely provided by individualsensory elements located throughout the system. As is shown by themonitoring and control system block diagram of FIG. 3, data collected bythe sensing units located within the closed loop system are fed to acentral programmable controller, which provides output data to theonstream operator as well as providing diagnostic information during andafter operation of the power pack. In addition, the programmablecontroller provides a fail/safe response to the data, individually orcombined, received from the various sensing elements, in the event thedata are outside of the prescribed range of values.

Specifically, the preferred logic control system receives sensory datainput from the inlet pressure sensors 20,21 for the oxygen/hydrogenmakeup supply gases, respectively, from upstream of the initial pressureregulators 24,25, as well as from downstream of the pressure regulators,by sensors 27,28. It has been found, however, that these sensorylocations are not among those required to optimize the system.

Those critical sensory locations for providing data to themicroprocessor system, which are the minimum necessary to achieveautomatic microprocessor control of the closed loop fuel cell powerpackage of this invention, include pressure sensors 39,40 in thehydrogen and oxygen fuel cell inlet lines, respectively, immediatelyupstream of the inlet to the fuel cell stack. The other necessarysensing locations for providing input data to the central controllerinclude the following: the gas flow sensors 60,61 (volumetricmeasurement at STP) in the recycle oxygen and hydrogen exit lines 50,51,respectively, from the stack 12, immediately downstream of therepressurization pumps 54,55; the temperature sensor 72 and water flowsensor 68 measuring the cooling water outlet temperature and volumetricflow rate in the water exit line 70 from the fuel cell stack internalcooling system; and the water level within the water knockout reservoirs30,31 as measured by the water level indicators 90,91, respectively.These data signals are sent to the central logic control system

Although the primary concern with respect to the water level in thereservoirs 30,31 is flooding, of the water reservoirs 30,31, and thusblocking of the gas flows in and out of the fuel cell through the oxygenand hydrogen gas lines 33,50,34,51, it is also important to maintain aminimum water level in order to insure there is adequate cooling andhumidification, or water saturation, of the gases flowing into the fuelcell stack. As previously explained, humidification is necessary inorder to maintain the integrity of the membrane electrolyte.

For security reasons, a flood sensor 93 is preferably provided toindicate if there is any liquid flooding into the power packagecontainer 10 and hydrogen gas detectors to note the presence ofexplosive hydrogen gas within the package container 10, outside of thefuel cell stack closed gas loop. Finally, the control system must haveinput from the sensory elements 125 measuring total fuel cell stackvoltage output as well as voltage output measurements for selectedindividual groups of cells within the stack; the selection of the groupsof cells to be combined to check voltage output is determined by eachindividual manufacturer, who provide voltage taps on the exterior of thefuel cell stack shell 12, for such data sensing. Generally, a single,multi-pin electrical outlet is provided for the output tap for thevarious voltage measurements.

The control system further provides for automatic operation of thesystem so as to shut down the system in the event sensory data indicatespotentially dangerous conditions. The data are recorded and comparedwith standard values, programmed into the programmable logic controller120, as parameters for the evaluation of the system. Thus, if certainprogrammable values are not met by the received data, the programmablecontroller is set to deactivate this system by activating the followingfunctions: disconnecting the electrical load from the fuel cell; closingthe solenoid inlet gas valves 17,18, thus shutting off makeup oxygen andhydrogen gases, respectively, from entering into the system; whilecontinuing to leave open the gas recirculation lines 50,51, and 35,34,including operation of the recycle pumps 54,55, for a sufficient time topermit the removal of condensate from the fuel cell stack, and to lowerthe fuel cell stack temperature by continuing the operation of thecooling water flow by maintaining the water pump 65.

In addition, the controller system is able, by programmable feedbackoperations, to increase makeup gas flow by controlling the pressureregulator valves 24,25, and can control the temperature within the fuelcell by activating the bypass valve 96 in the cooling water line to passthe water flow through the external heat exchanger 75, or through theshunt line 98 for recycling directly back to the water reservoir 30.

The closed loop system herein described is self-regulating over a majorportion of its operating range. The inlet pressure regulators 24,25respond to demand from the fuel cell to provide sufficient flow tomaintain the desired pressure drop within the system, between the inlets39,40 and the fuel cell outlets 50,51, as the gases are converted towater. The recycle flow rate is thus determined solely by the action ofthe repressurization pumps 54,55, or other means.

The repressurization recycle flow pumps 54,55 are generally maintainedfor constant recycle flow during the operation of the fuel cell.Generally the recycle is varied only downwardly if the cell is to beoperated at idle, i.e., at extremely low power outputs, to minimizehotel power requirements.

The container 10, packaging the fuel cell stack and the closed loopsystem is fluid and pressure-tight so as to substantially exclude fromwithin the container any pressure changes in the surrounding ambientconditions. All piping penetrating the container shell 10 generally passthrough the end bulkheads 85,86, for providing the necessary inputs andoutputs of data, control signals, reactants, water and electrical power.

Suitable microprocessor control systems are conventionally andcommercially available; such systems are preferably programmable by anyof the available binary logic programming or operating systems. Thecentral processing unit of the controller system must have sufficientmemory and operating capacity so as to register and record reactantsupply pressures, total cell voltage output, the voltage output fromgroups of cells and the cooling water temperature and flow. One suchuseful system is manufactured by Gould Electronics and designatedPC-0085. The present system, as depicted in the accompanying drawings,requires the ability to register, record and react to at least 12 datainput sources and must be capable of acting upon at least 6 operatingdevices. other suitable programmable controllers include the TSX17manufactured by Telemecanique; the Omran C-20K programmable controllerby Allen-Bradley, a division of Rockwell International; the GeneralElectric Company's Series 90-30 programmable controllers are also usablein the present system.

The materials of construction for the various plumbing and mechanicalcomponents useful in the closed loop management system of the presentinvention must be of sufficient structural strength to support anduphold the integrity of this system, and must be chemicallynon-interfering with the system. Generally, this requires that none ofthose materials of construction which are in any way exposed to thereactant gases or to the cooling water within the system, release freeions into solution or otherwise react with hydrogen or oxygen under theoperating conditions. Useful such materials which are thus inert to theworking fluids of hydrogen/oxygen and deionized water include thefollowing: 316 passivated stainless steel, fluorochlorohydrocarbons,such as Teflon, Viton polymers, polycarbonates, and silicon glass.Buna-N polymers and natural rubber, as well as all copper-containingmetal alloys are expressly excluded. The piping connections should bewelded and closed with O-ring face seals.

The reactant gases, preferably at least 99.9% pure hydrogen and medicalgrade oxygen, should be maintained at a pressure of not less than about100 psig. Pressurized "bottles", which are commercially available,generally are rated at pressures of from about 2000 to 2500 psig. Eachof these bottles should be provided with manual shutoff valves. Inaddition to such bottles of highly pressurized gases, other means ofstoring hydrogen include, for example, materials which are chemicallyreactive to form hydrogen, such as metal hydrides or methanol, orcryogenic storage devices; these are known and do not constitute a partof this invention.

The solenoid shutoff valves 17,18 are designed to be fail closed, i.e.,they shut off flow when a power interruption occurs or power isintentionally removed. Generally, pressure regulator valves should besuitable for use across the full range of pressures of the storagedevices and the minimum pressure required for fuel cell powerproduction. The pressure and flow sensors can either be of the minimumor maximum signalling type, or can provide quantitative values on acontinuing basis.

The water reservoirs 30,31 must be capable of withstanding a pressure ofnot less than 150% of the maximum fuel cell pressure. Theheight-to-width ratio of the reservoirs is preferably not less than 1.5,in order to provide for the desired free space above the top waterlevel. The oxygen reservoir, in which is collected the product waterfrom the fuel cell and which holds the deionized cooling water, shouldhave a total volume of at least about 0.5 liters of deionized water perkW-hour output rating for the fuel cell stack or stacks, with a freespace below the gas lines 34,51 of at least about 4 ins. The hydrogenreservoir should hold at least about 50 mls of water per kW-hour maximumoutput power rating. Initially, at startup, there need be provided inthe reservoirs 30,31 only sufficient water to provide the requiredhumidification of the reactant gases and cooling of the stack.

The recirculating gas pumps 54,55 in the hydrogen and oxygen recyclelines, respectively, must provide a discharge pressure at leastsufficient to start against the maximum fuel cell rated pressure. Thepumps can be any of the centrifugal, diaphragm or positive displacementtype pumps, formed of suitable materials of construction.

The water recirculation pump similarly can be of any commerciallyavailable type, again formed from suitable materials of construction toavoid any transfer of ions into solution in the flowing cooling water.

The recirculation pumps 54,55 for the reactant gases, as explainedabove, can be substituted with an eductor-type system utilizing thepressure drops and flow between the, e.g., gas supply bottles, and thefuel cell inlets. By this means, additional power savings are obtained;generally the flow of gases to the fuel cell is more than adequate toprovide the needed energy for the recirculation pressurization.

The electrical connections between the various sensory and operationallocations within the power package container 10 and the microprocessorcontrol system 120 are in accordance with conventional standards forexplosion proof systems. The only requirement, except for suitableconductivity, revolves about the safety requirement when dealing withhydrogen gas. Generally, commonly available such control systems areadequately insulated and of sufficiently low power that there should beno danger of explosion, even if hydrogen gas is released into theenvironment.

The fuel cell stack power output is tapped off through the powerconnector 130, passing through the container end plate 86.

EXAMPLE

The enclosed modular container system depicted in FIG. 4 was utilized asthe auxiliary power system for a research submersible. The outercontainer 10 had a internal diameter of 15 inches and a total internallength of 72 inches. The outer shell was capable of withstanding apressure differential of 450 PSI across its walls.

Hydrogen and oxygen gas bottles at a pressure of 2250 PSIG were attachedto the gas supply valves 4,5. The fuel cell stack is an availableBallard Mark V, 5 kilowatt hydrogen/oxygen fuel cell stack with a solidpolymer electrolyte. At steady state operation, the recycle hydrogenflow through line 51 is 9 liters per minute STP and the recycle flow ofoxygen through line 50 is 9 liters per minute STP. The repressurizationpumps 54, 55 are rated to increase the pressure from 28 psig to 30 psigand the water reservoirs have a total internal capacity of 10 liters forthe oxygen reservoir 30 and 1 liter for the hydrogen reservoir 31. Theamount of water should not be greater than 8 liters for the oxygenreservoir 30 0.75 liters for the hydrogen reservoir 31. The coolingwater flow at steady state operation as measured by the liquid flowmeter 68 is 6.5 liters per minute. When operating in sea water having atemperature of 80'F. The heat exchanger has a heat exchange surface areaof 57 sq. in.

The pressure of the reactant gases at the pressure sensors 20, 21 isadjusted to be 30 psig.

This fuel cell system can operate continuously for at least 3 hoursdepending upon the amount of hydrogen and oxygen reactants provided. Thetotal volume within the close loop system is sufficiently great that anyaccumulation of inerts which may be present in the reactant gas supplyor which may result from operation of the system do not accumulate insufficient concentration to interfere with the fuel cells operation.This fully enclosed and compact system is thus especially valuable forthose situations where these attributes are valuable, such as forsubmersibles or spacecraft.

The patentable embodiments of this invention which are claimed are asfollows:
 1. A closed loop reactant/product management system forelectro-chemical galvanic energy devices, the system comprising:a. fuelcell means comprising first and second internal reactant gas conduitmeans, and internal coolant liquid conduit means; b. first and secondreactant gas supply connecting means; first inlet line means forpressure-tight gas flow connection from said first reactant gas supplyconnecting means to said first internal reactant gas conduit means;second inlet line means for pressure-tight gas flow connection from saidsecond reactant gas supply connecting means to said second internalreactant gas conduit means; c. indirect heat exchanger means in fluidflow connection with the internal liquid flow conduit means; d. firstliquid-gas separator and liquid reservoir means in pressure-tight fluidflow connection with the heat exchanger means and with the internalliquid flow conduit means and with the first internal gas flow conduitmeans; e. second liquid-gas separator and liquid reservoir means inpressure-tight fluid flow connection with said second internal gas flowconduit means; f. first gas repressurization means between said firstliquid-gas separator means and said first internal reactant gas conduitmeans to increase the pressure of the first gas applied to said firstinternal gas flow conduit means; and g. second gas repressurizationmeans between said second liquid-gas separation means and said secondinternal reactant gas conduit means to increase the pressure of thesecond gas applied to said second internal gas flow conduit means.
 2. Aclosed loop reactant/product management system according to claim 1,wherein said first gas repressurization means pressurizes said first gasto the same pressure as said first reactant gas supply connecting meansprovides for the first gas it supplies as the make-up first gas; andsaid second gas repressurization means pressures said second gas to thesame pressure as said second reactant gas supply connecting meansprovides for the second gas it supplies as the make-up second gas.
 3. Aclosed loop reactant/product management system according to claim 2,further comprising a repressurization means between said firstliquid-gas separation means and said internal liquid flow conduit meansto increase the flow of liquid from said first liquid-gas separationmeans to said fuel cell means.
 4. A closed loop reactant/productmanagement system according to claim 2, further providing a selectivelyoperable shunt to permit liquid to by-pass said indirect heat exchangermeans and be returned to said internal liquid flow conduit means at ahigher temperature than would be possible if the liquid passed throughthe heat exchanger.